The direct acquisition algorithm of GPS P-code under low-SNR and large Doppler frequency is studied and analyzed in this paper. Direct average method, matched filtering method and partial correlated method based on FFT are all simulated and compared with each other according to the performance and realization of the acquisition. Through the contrast we can see that, partial correlated method based on FFT transform 2-D to 1-D. It has the ability of anti-noise and faster acquisition time, so more suitable for engineering.